This project is the continuation of the studies supported by the previous grant n degrees RO1 DE04257. By using a stable cell marking technique the migration pattern and the developmental fate of neural crest cells could be followed in topical chimeras in avian embryos. It appeared that the NC plays a major role in head and neck morphogenesis through a massive migration of cells from the cephalic crest to the facial and hypobranchial area. Our further studies will concern the relationships between cell migration, proliferation and organogenesis in the mesectodermal derivatives of the face. This will be carried out by combining the cell marking technique with autohistoradiography and various cytochemical approaches. The evolution of the peripheral nervous system, already extensively studied during the past few years by our group will be continued. Determination and differentiation of the ganglion cells of the peripheral nervous system in the head and the other parts of the body will be investigated by means a variety of experimental approaches involving in vivo transplantation, in vitro culture, biochemical and cytochemical techniques. The factors responsible for the segregation of the various cell lines derived from the NC will especially retain our attention.